Tambour or roll-top door concepts are used in certain furniture such as roll-top desks, in certain trucks and garages, in curtains in theatres. Such tambour door concepts or structures provide a compact means for closing a space without requiring a typical one-piece door that swings in an arc about a hinge; furthermore a tambour door, when opened, may be slid into a recess within the assembly where it is conveniently hidden. Another feature of these doors is the potential attractiveness made possible by the plurality of separate segments hinged together.
It should be noted that in the typical applications described above, these tambour doors slide in a curved track from a first closed position wherein the segments are aligned as a generally vertical wall, upward around a curved portion of the track, to an open position wherein the segments are aligned in a generally horizontal or other orientation. In many instances these doors are quite large and heavy and consequently are difficult to move; in particular it is difficult to get the door started in its movement and equally difficult to stop the door after it has begun moving due to the high inertia force. Very heavy doors may be impossible to move by hand without supplemental spring or motor drive means, and similarly it may be impossible to stop the doors and prevent a crashing impact without supplemental means. Furthermore it may be quite dangerous for such doors to be operated without means to prevent uncontrolled movement once they are started in their movement.
The prior art solutions to the above described problems involve a variety of different counter-balancing or counter-weight mechanisms which attempt to set up a force which is generally equal to the weight of the door, so that movement of the door is possible by the addition of a very small additional force to simply unbalance the counter-weighted system. Counter-weighting can be done in the simple manner of having a pulley arrangement with an actual weight posed in opposition to the weight of the door. Also a variety of springs may be considered, however the normal problem with springs is that they tend to develop greater resistance with greater extension according to Hooke's law. Accordingly a spring would provide different forces depending upon the position of the door, and consequently such systems sometimes use two or more springs each operable at different positions of the door, as means for pre-loading the door to be at least partially counter-balanced. The descriptions herein concern doors that are manually operated; in the case of power driven doors, the drive mechanism may or may not include inherent brake features which would make it unnecessary to pre-load a door to prevent it from moving after the driving force has stopped.
In a still different arrangement, there are compression springs arranged to engage a lever on the door when it has arrived at either of its extreme closed or open positions; the engagement occurs as the door approaches the final position whereupon a spring is compressed, thus cushioning the door from impacting at the time of closing or opening. This is particularly useful for theatre curtains where it is important to avoid a loud thud or crashing noise when the curtain falls.
In summary, the prior art spring mechanisms tend to be operable only during part of the door's travel until the spring becomes wound or flexed, or else a complex arrangement of multiple springs with means to disengage them at appropriate times is required; alternatively pulley arrangements with weights are required to truly counter-balance the door at all times. The present invention provides a new mechanism and arrangement for counter-balancing the door at all positions of its travel and thus providing the benefits of a counter-balanced pulley system and a pre-loaded spring system; very little force is required to initiate or maintain movement of the door in either direction, and the door is counter-balanced between its own weight and the spring force causing it to remain relatively stable when no external force is applied. A summary of the new invention and a detailed description of the preferred embodiment thereof follows below.